LiDAR sensor with orthogonal arrays

ABSTRACT

An apparatus for scanning a scene comprising a light transmitter including a one-dimensional phased array; wherein the light transmitter is fed by a frequency swept scanning laser; and a light receiver including a one-dimensional phased array; the one-dimensional phased array of the light receiver disposed orthogonally to the one-dimensional phased array of the transmitter; wherein light received by the light receiver is enabled to be interfered with light from the frequency swept scanning laser.

RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. § 119(e) ofU.S. Patent Application Ser. No. 62/547,714 filed Aug. 18, 2017 andentitled “STEERING A BEAM WITH A GRATING,” which is hereby incorporatedherein by reference in its entirety. This present application is alsorelated to U.S. patent application Ser. No. 16/104,866 filed on Aug. 17,2018 and entitled “A METHOD, SYSTEM, AND APPARATUS FOR A LIDAR SENSORWITH A LARGE GRATING,” and patent application Ser. No. 16/104,869 filedon Aug. 17, 2018 and entitled “METHOD, APPARATUS, AND SYSTEM FOR LIDARSENSOR WITH VARYING GRATING PITCH,” which are both hereby incorporatedherein by reference in their entirety.

BACKGROUND

Scanning systems often transmit a signal and measure a reflection of thesignal at a receiver.

BRIEF DESCRIPTION OF THE FIGURES

Various aspects and embodiments of the application will be describedwith reference to the following example embodiments. It should beappreciated that the figures are not necessarily drawn to scale.

FIG. 1 is a simplified illustration of an optical scanning system with atransmitter and receiver using an array of phase shifters to steer atransmitter beam, in accordance with an embodiment of the presentdisclosure;

FIG. 2 is an alternative simplified illustration of an optical scanningsystem with a transmitter and receiver in which gratings of atransmitter and receiver have a same orientation, in accordance with anembodiment of the present disclosure;

FIG. 3 is a simplified illustration of optical scanning using an opticalscanning system, in accordance with an embodiment of the presentdisclosure;

FIG. 4a is a simplified illustration of a transmitter array and areceiver array, in accordance with an embodiment of the presentdisclosure;

FIG. 4b is a simplified illustration of two transmitter arrays and tworeceiver arrays, in accordance with an embodiment of the presentdisclosure;

FIG. 4c is an alternative simplified illustration of two transmitterarrays and two receiver arrays, in accordance with an embodiment of thepresent disclosure;

FIG. 4d is a further simplified illustration of two transmitter arraysand two receiver arrays with a waveplate, in accordance with anembodiment of the present disclosure;

FIG. 5 is a simplified method for creating an optical scan, inaccordance with an embodiment of the present disclosure;

FIG. 6 is an alternative simplified method for creating an optical scan,in accordance with an embodiment of the present disclosure; and

FIG. 7 is a simplified illustration of optical scanning using an opticalscanning system showing scanning ellipses in a 3 dimensional scene, inaccordance with an embodiment of the present disclosure.

SUMMARY

A method and apparatus for scanning a scene.

DETAILED DESCRIPTION

Generally, a LiDAR scanning system may be used to capture a 3D image ofa scene. Typically, there may be a transmitter (Tx) that projects lightand a receiver (Rx) that receives the reflection of the light. Inconventional systems, a Tx scans a beam in 2D using a moveable mirror.Generally, a moveable mirror is expensive, and prone to reliabilityissues, cannot sweep very fast, and requires high voltages. In manyembodiments, the current disclosure has recognized that there may bebenefits to “solid state” scanning that eliminates a moveable mirror.Note that in the marketplace, some LiDAR systems with MEMS moveablemirrors are called “solid state.” In many embodiments herein, the use of“solid state” herein, implies no moving parts.

The current disclosure has recognized that conventional 2D solid statesolutions, such as a 2D phased array of gratings, may be complex anddifficult to scale because of the requirement for a large number ofcontrollable elements such as a 2D phased array of gratings. Typically,a 2D solid state scanner may use controllable elements to steer in onedirection and laser wavelength tuning to steer in another direction. Inmany embodiments, the current disclosure recognizes that if wavelengthtuning is used to steer direction, using wavelength to measure depth islimited or not possible. Also, using wavelength to steer typicallyrequires a large tuning range from the laser, which makes the laserabout 10 times more expensive.

In some embodiments, a 1D scanner may be simpler to make and may bescalable to a large scanning range and high resolution. In someembodiments, a 1D scanner may use a MEMS mirror scanning in onedimension for the Tx and a lens and receiver array for the Rx, where theRx array is orthogonal to the Tx scanning direction. In anotherembodiment, a 1D scanner may use an array of 1D phased arrays, pointingat different angles in an orthogonal direction to the steering, in orderto create 2D scanning.

Typically, scanning performed in 1D is performed with pulsed ormodulated light and direct detection to determine distance. Generally,direct detection is used to detect reflected light. In many embodiments,the current disclosure has realized that direct detection may result ina limited resolution of a scan. In most embodiments, the currentdisclosure has realized that direct detection may be able to measure onephoton at a time, with a single photon APD (SPAPD), which may limitdetection if multiple photons are reflected from a given point due tothe recovery time of the SPAPD.

In almost all embodiments, the current disclosure has realized thattypical systems that use non-coherent light may not function well withpartial reflections. In certain embodiments, the current disclosure hasrecognized that typical direct detect systems may not work well withtrees where there may be partial reflections. In other embodiments, thecurrent disclosure has realized that direct detect systems may besensitive to interference from transmission from other direct detectsystems.

In certain embodiments, the current disclosure may enable using coherentlight with a one dimensional array to perform scanning of a scene. Inmany embodiments, the current disclosures may enable using onedimensional scanning to realize a three-dimensional image. In someembodiments, the current disclosures may enable using one dimensionalscanning to realize a four-dimensional image, where the fourth dimensionindicates motion. In certain embodiments, the current disclosure mayenable a point spread of a three-dimensional scene. In some embodiments,a point spread of a scene may be called a point cloud.

In certain embodiments, the current disclosure may use coherent light tocreate a point cloud of a scene. In many embodiments, use of coherentlight may enable a resolution around 100 times better than using adirect detect system. In some embodiments, a coherent detection systemmay offer a distance resolution of microns. In other embodiments, use ofcoherent light may offer tens of centimeters of distance. In certainembodiments, coherent light may refer to light of a similar or uniformwavelength and phase, such as that produced by a laser. In someembodiments, incoherent light may refer to light that has differentphases or waves such as light produced by a lightbulb.

In most embodiments, use of coherent light may be resilient againstinterference of other light sources. In many embodiments, a coherentlight scanning system may filter out light other than the frequency of acoherent light scan. In certain embodiments, a coherent scanning systemmay not receive interference from other light sources from anothercoherent scanning system unless the laser sweeps of the systems aresynchronized. In many embodiments, a coherent system may be able toenable four-dimensional scanning, location plus movement, by measuring aDoppler shift or upshift in the frequency of the received light.

In certain embodiments, the current disclosure may enable a LiDAR sensorthat uses orthogonal 1D transmitter and receiver arrays and wavelengthsweeping to create a 3D image. In many embodiments, a transmitter arraymay project light using an array of phase shifters and shortsurface-emitting gratings. In many embodiments, a phased array may meanoptical emitters or receivers with a controllable phase for eachelement. In most embodiments, a phased shifter may be an optical elementthat can adjust phase of light. In certain embodiments, a grating may bean optical element with periodic spaced scattering elements.

In most embodiments, the current disclosure may use an array of coherentreceivers to detect light from a transmitter. In many embodiments, acoherent receiver may be able to measure phase and thus may be able todetermine direction of a 1-direction beam. In most embodiments, byanalyzing speed of interference fringes in relation to a sweeping speedof a laser, a distance may be calculated.

In many embodiments, the current disclosure may enable two orthogonal 1Dphased arrays, one acting as a Tx and the other as an Rx. In someembodiments, a Tx may be steered using controllable elements. In manyembodiments, a Rx may be an array of coherent receivers. In someembodiments, a coherent receiver may measure phase and may distinguishfrom which direction, in 1D, the beam is coming. In many embodiments,input to the Tx may be a frequency-swept laser, and part may be splitoff to act as a local oscillator for the coherent receiver array. Incertain embodiments, by analyzing the speed of the interference fringesin relation to the sweeping speed of the laser, the distance may becalculated. In many embodiments, the current disclosure has realizedthat conventional systems typically use direct detection and thus cannotuse a phased array for the Rx.

Refer now to the example embodiment of FIG. 1. In the example embodimentof FIG. 1, frequency-swept laser 105 feeds light to a transmitterthrough waveguide 107. The transmitter is fed by waveguide 107 intomodulator 109, which modulates the light, and transmits the lightthrough waveguides, such as waveguide 111 to phase shifters, such asphase shifter 113, phase shifter 115, and phase shifter 117. Phaseshifters 113, 115, and 117, shift the phase of the light and transmitthe light to transmitter grating through waveguides, such as waveguide121 and 123. Light flows through transmitter grating array 125 andilluminates a portion of a scene. In this embodiment, transmitter is aone dimensional transmitter. The transmitter consists of an array ofphase shifters and short surface-emitting gratings. FIG. 1 has waveguide130.

Laser 105 also feeds a local oscillator of a receiver. The receiverincludes receiver grating array 131, which feeds received light throughwaveguides, such as waveguides 133 and 135 to optical hybrids, such asoptical hybrids 137, 139, and 141. Optical hybrid 137 feeds photodiodes143 and 145, optical hybrid 139 feeds photodiode 147 and 149, andoptical hybrid 141 feeds photodiode 151 and 153. In this embodiment,receiver grating array 131 is orthogonal to transmitter grating array125. In the example embodiment of FIG. 1, optical hybrids 137, 139, and141 are 180° hybrids. The output of the photodiodes 143, 145, 147, 149,151, 153, is fed, directly or indirectly, into Digital Signal Processor(DSP) 160.

In some embodiments, 90° hybrids instead of 180° hybrids may be used ina receiver. In many embodiments, hybrids maybe connected to photodiodepairs. In another embodiment, one photodetector per hybrid may be usedin a receiver. In certain embodiments, photodiodes in each pair may besubtracted in a differential amplifier, and the resulting difference maybe digitized in an analog-to-digital converter, which may be fed into adigital signal processor (DSP).

In some embodiments, a DSP may recover magnitude and phase of the lightreceived by each surface grating. In most embodiments, by measuring afrequency of fringes of interference from a scanned object as a laserwavelength tunes, a DSP may determine distance to (i.e., depthinformation of) the reflection point of the scanned object.

In many embodiments, the transmitter and receiver may be part of aphotonic integrated circuit (PIC). In some embodiments, a transmitterand receiver may be on the same die or separate die. In certainembodiments, a PIC may be made in silicon photonics. In mostembodiments, silicon photonics may permit high-contrast gratings,efficient phase shifters, compact waveguide circuits, and integratedphotodiodes.

In many embodiments, phased array emitters may be short gratings. Incertain embodiments, a receiver may need to receive the samepolarization as emitted by a transmitter. In a particular embodiment, ahalf-wave plate may be placed over either a transmitter or receiverarray to rotate the polarization. In another embodiment, there may beorthogonal polarizations in transmitter and receiver waveguides, e.g.,TE polarization in the transmitter waveguides and TM polarization in thereceiver waveguides. In certain embodiments, polarization rotators andgrating designs may be used. In other embodiments, waveguides of atransmitter grating and a receiver grating may be bent so thepolarization of the received light is the same as the polarization ofthe transmitted light, such as shown in FIG. 2.

In the example embodiment of FIG. 2, frequency-swept laser 205 feedslight to a transmitter through waveguide 207. The transmitter is fed bywaveguide 207 into modulator 209, which modulates the light, andtransmits the light through waveguides, such as waveguide 211 to phaseshifters, such as phase shifter 214, phase shifter 215, and phaseshifter 216. Phase shifters 214, 215, and 216 shift the phase of thelight and transmit the light to transmitter grating through waveguides,such as waveguide 221 and 223. In this embodiment, the transmitter is aone dimensional transmitter. The transmitter consists of an array ofphase shifters and short surface-emitting gratings. FIG. 2 has waveguide230.

Laser 205 also feeds a local oscillator of a receiver. The receiverincludes receiver grating array 231, which feeds received light throughwaveguides, such as waveguides 233 and 235 to optical hybrids, such asoptical hybrids 237, 239, and 241. Optical hybrid 237 feeds photodiodes243 and 245, optical hybrid 239 feeds photodiode 247 and 249, andoptical hybrid 241 feeds photodiode 251 and 253. In the exampleembodiment of FIG. 2, optical hybrids 237, 239, and 241 are 180°hybrids. The output of the photodiodes 243, 245, 247, 249, 251, 253, isfed, directly or indirectly, into Digital Signal Processor (DSP) 260.

Refer now to the example embodiment of FIG. 2. The example embodiment ofFIG. 2 is similar to that of FIG. 1, however in the example embodimentof FIG. 2, waveguides of transmitter grating 225 and waveguides ofreceiver grating 231 are bent by 45 degrees before the gratings so thatthe gratings have the same orientation. In the example embodiment ofFIG. 2, bending the waveguides ensures that the receiver receives thesame polarization of light as transmitted by the receiver.

Refer now to the example embodiment of FIG. 3, which illustratesschematic of a scanning area and receiver area. In the exampleembodiment of FIG. 3, light from transmitter 310 has an ellipticalfar-field pattern 315, which can be steered side-to-side by adjustingphase shifters of Transmitter 310. Light transmitted by transmitter 310to ellipse 315 reflects off objects in the scene and falls on receiver320. Receiver 320 receives light from ellipse 325 in the far field thatscans in an orthogonal direction to transmitter ellipse 315. Withtransmitter 310 scanning in one lateral dimension, receiver 320 scanningin a second lateral dimension, and laser 330 scanning depth, a 3-D imagecan be captured. Note, in the example embodiment of FIG. 3 that thereceiver is not scanning. In the example embodiment of FIG. 3, thereceiver is receiving light simultaneously from all directions, and thecoherent signal processing determines where the light comes from in theRx “scanning” direction by examining the relative phases of the receivedlight between waveguides. In other embodiments, the Tx and Rx may eachbe rotated 90 degrees.

In some embodiments, received power may be a fraction of the transmittedpower. In particular embodiments, excess loss may be approximately equalto a resolution of scanning by the Tx. In the example embodiment of FIG.3, excess loss may be equal to the resolution of scanning in thevertical direction.

Refer now to the example embodiment of FIG. 4a , which illustrates atop-die-view general configuration of a transmitter and receivergrating. In FIG. 4a , a one-dimensional transmitter 400 array includesfeed waveguides 410 and 1-D grating 415. Orthogonal 1-D receiver array405 has feed waveguides 420 and one-dimensional grating 425. In thisexample embodiment, transmitter grating 400 and receiver grating 405 arelocated on a single PIC.

In FIG. 4b , there are multiple transmitter/receiver sets on the samePIC or PIC package, to improve light collection efficiency, improvescanning time, and/or improve signal-to-noise ratio. In FIG. 4b , thereare two transmitter arrays 453 and two receiver arrays, 451 and 452. Inthe example embodiment of FIG. 4b , the designation of transmitter arrayand receiver array may be changed so that a different array is areceiver array and a different array is a transmitter array.

Refer now to the example embodiment of FIG. 4c , which illustrates atop-die-view general configuration of a transmitter and receivergrating. In FIG. 4c , a one-dimensional transmitter 485 array includesfeed waveguides 484 and 1-D grating 486. Parallel 1-D receiver array 482has feed waveguides 481 and one-dimensional grating 483. In this exampleembodiment, transmitter grating 485 and receiver grating 482 are locatedon a single PIC. In an embodiment, the light transmitter and lightreceiver gratings are parallel to each other.

Refer now to the example embodiment of FIG. 4d , which illustrates atop-die-view general configuration of a transmitter and receivergrating. In FIG. 4d , a one-dimensional transmitter 491 array includesfeed waveguides 490 and 1-D grating 492. Orthogonal 1-D receiver array487 has feed waveguides 488 and one-dimensional grating 489. In thisexample embodiment, transmitter grating 492 and receiver grating 489 arelocated on a single PIC. Waveplate 493 rotates polarization of the lightreceiver. In an embodiment, wherein the light transmitter and lightreceiver gratings are oriented orthogonal to each other, there is awaveplate to rotate the polarization of the light transmitter. In anembodiment, wherein the light transmitter and light receiver gratingsare oriented orthogonal to each other, there is a waveplate to rotatethe polarization of the light receiver.

Refer now to the example embodiment of FIG. 5, which illustrates asample method for scanning a scene. A transmitter, such as for exampleone of FIGS. 1-4, transmits light (step 505). A receiver, such as forexample, a receiver of FIGS. 1-4, receives the reflection of thetransmitted light (step 510). The system is steered to capture anotherportion of the scene (step 515). In most embodiments, steering thesystem may include changing where the transmitter is projecting lightand where the receiver is expecting to find reflected light.

Refer now to the example embodiment of FIG. 6, which illustrates asample method for creating a point cloud. Light is transmitted orprojected by a transmitter, such as for example of that of FIGS. 1-4(step 600). A receiver, such as for example, a receiver of FIGS. 1-4,receives the reflection of the transmitted light (step 610). Thelocation the receiver is expecting to receive light is changed (Step610). The transmitter is steered (step 615) and steps 600-615 areiterated to scan a scene. Light received from the reflection isprocessed by a digital signal processor, such as for example the DSP ofFIG. 1 or 2 (step 620). A point cloud is created (step 625). In certainembodiments, a DSP may control the steering of the scanning system. Inmany embodiments, a DSP may be able to determine motion of an object bymeasuring the Doppler effect for a received point. In some embodiments,a DSP may be able to determine whether a point received is a liquid bymeasuring a Doppler effect for a received point.

Refer now to the example embodiment of FIG. 7, which illustrates anoptical scanning system showing scanning ellipses in a 3 dimensionalscene. In the example embodiment of FIG. 7, scene 700 is a threedimensional scene. Scene 700 is demarked by z axis 701, y axis 702, andx axis 703. PIC 705 is aligned as a plane across x axis 703. PIC 710 hastransmitter grating 720. Transmitter grating 720 illuminates transmitterellipse 725 in scene 700. PIC 705 has receiver grating 710 whichreceives light from area shown as receiver ellipse 715. Ellipse overlap730 is where transmitter ellipse 725 and receiver ellipse 715 overlapand denotes the portion of reflected light from transmitter grating 720that receiver grating 710 receives and processes.

In many embodiments, techniques of the current disclosure may require nomoving parts (not even a MEMS mirror), may be very compact, and may bescalable to very high-resolution scans. In certain embodiments, theremay be a relatively low collection efficiency by the receiver, becausethe ellipse of the receiver is orthogonal to that of the transmitter. Inmost embodiments, collection efficiency may be irrelevant as the lighttransmitted is outside of a range that can impact human vision. In manyembodiments, the power of the light used may not be a safety concern asit may be outside the range of light that is harmful to human vision. Insome embodiments, the wavelength of the light may be in the range of1550 nm. In certain embodiments, an ellipse transmission are may lowerthe power of light such that it is not harmful to human vision.

In many embodiments, one or more of the current techniques may beperformed on a Digital Signal Processing (DSP) of a receiver. In mostembodiments, the output of a scanning system may be sent to a DSP. Incertain embodiments, a DSP may process the captured light to determine apoint cloud. In many embodiments, a DSP may be a custom designed ASICchip in order to process measured light quickly and power efficiently.In most embodiments, a DSP may be able to determine change in thewavelength of reflected light. In many embodiments, a DSP may be able todetect change of phase of reflected light. In certain embodiments, a DSPmay be able to detect other changes in the reflected light. In almostall embodiments, a DSP may be able to determine distance by looking atchanges in reflected light. In many embodiments, a DSP may be able todetermine location within three dimensions by looking at reflectedlight.

In some embodiments, one or more of the techniques described herein maybe stored on a computer readable medium. In certain embodiments, acomputer readable medium may be one or more memories, one or more harddrives, one or more flash drives, one or more compact disk drives, orany other type of computer readable medium. In certain embodiments, oneor more of the embodiments described herein may be embodied in acomputer program product that may enable a processor to execute theembodiments. In many embodiments, one or more of the embodimentsdescribed herein may be executed on at least a portion of a processor.

In most embodiments, a processor may be a physical or virtual processor.In other embodiments, a virtual processor may be spread across one ormore portions of one or more physical processors. In certainembodiments, one or more of the techniques or embodiments describedherein may be embodied in hardware such as a Digital Signal ProcessorDSP. In certain embodiments, one or more of the embodiments herein maybe executed on a DSP. One or more of the techniques herein may beprogramed into a DSP. One or more of the techniques herein may befabricated in a DSP. In some embodiments, a DSP may have one or moreprocessors and one or more memories. In certain embodiments, a DSP mayhave one or more computer readable storages. In other embodiments, oneor more of the embodiments stored on a computer readable medium may beloaded into a processor and executed.

Having thus described several aspects and embodiments of the technologyof this application, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those of ordinaryskill in the art. Such alterations, modifications, and improvements areintended to be within the spirit and scope of the technology describedin the application. It is, therefore, to be understood that theforegoing embodiments are presented by way of example only and that,within the scope of the appended claims and equivalents thereto,inventive embodiments may be practiced otherwise than as specificallydescribed. In addition, any combination of two or more features,systems, articles, materials, and/or methods described herein, if suchfeatures, systems, articles, materials, and/or methods are not mutuallyinconsistent, is included within the scope of the present disclosure.

Also, as described, some aspects may be embodied as one or more methods.The acts performed as part of the method may be ordered in any suitableway. Accordingly, embodiments may be constructed in which acts areperformed in an order different than illustrated, which may includeperforming some acts simultaneously, even though shown as sequentialacts in illustrative embodiments.

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified.

The terms “approximately” and “about” may be used to mean within ±20% ofa target value in some embodiments, within ±10% of a target value insome embodiments, within ±5% of a target value in some embodiments, andyet within ±2% of a target value in some embodiments. The terms“approximately” and “about” may include the target value.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. The transitional phrases “consisting of” and “consisting essentiallyof” shall be closed or semi-closed transitional phrases, respectively.

The terms “approximately” and “about” may be used to mean within ±20% ofa target value in some embodiments, within ±10% of a target value insome embodiments, within ±5% of a target value in some embodiments, orwithin ±2% of a target value in some embodiments. The terms“approximately” and “about” may include the target value.

What is claimed is:
 1. An apparatus for scanning a scene comprising: acoherent light transmitter including a transmitter one-dimensionalphased array; wherein the coherent light transmitter is fed by afrequency swept scanning laser; a coherent light receiver including areceiver one-dimensional array; and an array of optical hybrids; anarray of photodetectors; the receiver one-dimensional array disposedorthogonally to the transmitter one-dimensional phased array; whereinlight received by the coherent light receiver is enabled to beinterfered with light from the frequency swept scanning laser in thearray of optical hybrids by interfering light received individually ineach element of the receiver one-dimensional array with light split offfrom the frequency swept scanning laser; wherein each individuallyinterfered light is sent to at least a respective photodiode of thearray of photodetectors.
 2. The apparatus of claim 1 wherein the phasedarray of the coherent light transmitter further includes surfaceemitting gratings; wherein the phased array of the coherent lightreceiver further consists of surface emitting gratings.
 3. The apparatusof claim 2 wherein each photodetector of the array of photodetectors isa photodiode; array wherein each optical hybrid of the array of opticalhybrids has a balanced photodiode pair.
 4. The apparatus of claim 1wherein the one-dimensional phased array of the coherent lighttransmitter is a phased array of phase shifters.
 5. The apparatus ofclaim 1 wherein measurements of light received by the coherent lightreceiver are sent to a digital signal processor (DSP); wherein the DSPgenerates a point cloud of a scene from which the light reflected. 6.The apparatus of claim 1 wherein the coherent light transmitter and thecoherent light receiver are on the same photonic integrated circuit. 7.The apparatus of claim 1 wherein the coherent light transmitter and thecoherent light receiver employ gratings.
 8. The apparatus of claim 7wherein the coherent light transmitter and coherent light receivergratings are oriented orthogonal to each other and there is a waveplateto rotate the polarization of the coherent light transmitter or coherentlight receiver.
 9. The apparatus of claim 7 wherein the coherent lighttransmitter and coherent light receiver gratings are parallel to eachother and there are waveguide bends connecting the gratings to thearrays of waveguides.